1. Technical Field
This invention relates to propylene polymers and more particularly to polypropylenes useful for applications requiring good clarity.
2. Background of the Art
Propylene-based polymers are finding increasing numbers of applications in the thermoplastics industry. These polymers offer relatively good strength and other performance properties when used in applications such as, for example, disposable food containers. Unfortunately, injection molded articles prepared from Ziegler-Natta catalyzed isotactic polypropylene homopolymers often have a hazy or cloudy appearance. The haziness or cloudiness tends to increase as the thickness of the molded part increases, which often renders these materials less desirable for use in preparing injection molded articles.
Clarity-enhancing agents may be used in attempts to counter this haze problem. Such are usually added to the melted polymer either in the formation of pellets or prior to injection of the polymer into the mold. In general, clarity-enhancing agents provide a site within the polymer resin for crystallization to occur. This allows smaller crystallites to form, which, in turn, allows light to travel through the polymer medium, rather than be diffracted. While clarity-enhancing agents may be helpful, such are often relatively expensive and thus, their use is desirably minimized.
Thus, it would be desirable in the art to identify polypropylene materials that exhibit improved clarity or gloss, with or without the use of clarity-enhancing agents.